This invention is directed for use in a system for supplying air to a clean room which is filtered to remove substantially all dust and/or bacteria or the like.
In general it has been found that it is preferred that the air enter a clean room from above and pass through filters located in the ceiling. Appropriate ducts are provided at the floor of the room for recirculating or for exhausting the air from the room. Suitable air sources and fans are provided as part of the system to keep the air moving so that clean air is always coming into the room and the old contaminated air is being expelled.
Air filter media having extremely high efficiencies on submicron sized particles have been developed for use in this manner and are generally referred to in the industry as "HEPA" filters. These filter media may comprise or include glass, ceramic or cellulose papers which have the ability to remove a high percentage of the defined particles. Generally the paper media is pleated in accordian fashion and mounted within and sealed along the edges of a frame to form a filter.
Conventionally, overhead air filtering systems are constructed in modular form. Typically a series of rigid supporting frames are mounted in some fashion above the room and form a latticework of rectangular openings through which the air enters the room. These openings are covered with the HEPA filters through which all of the air must pass before entering the room. The greatest problem encountered in systems of this nature is the leakage of air between the support frame and the filter media so it does not get filtered before entering the room. One of the solutions to this problem is an overhead air filtering system disclosed in U.S. Pat. No. 3,486,311 titled "Filter Bank Assembly" by Allan. The Allan assembly provides the overhead latticework of support frames in the form of U-shaped channels which are all interconnected with one another. The channels are filled with a liquid or semiliquid material and the filter is constructed so that the side walls of the filter frame have vertically extended edges which rest in the liquid material contained in the supporting channels. While this system serves the purpose of preventing air leakage around the frame of the filter, it does have its drawbacks. For one, the channels must be tested for liquid leakage and in a large installation leaks may occur even after testing so that fluid if not at least partly solidified, could leak out of the channel and create problems. Another drawback is that the support channels cannot be used for attaching other devices such as light fixtures or sprinkler systems or the like. In addition, it is quite messy to replace and reset a filter.